In a brutal battle against the demons to reclaim their territory, humanity’s strongest warrior, Arthur King, is killed at the final moment when he is caught in the Demon King’s blast, only to be reborn as one of them through a mysterious system. Due to a system error, he has no choice but to die again to return to the human world. He throws himself into deadly situations, but fate twists against him, and every attempt at self-destruction pulls him deeper into the demon world.